Thermal barrier coating resistant to sintering

ABSTRACT

A device ( 10 ) is made, having a ceramic thermal barrier coating layer ( 16 ) characterized by a microstructure having gaps ( 18 ) with a sintering inhibiting material ( 22 ) disposed on the columns ( 20 ) within the gaps ( 18 ). The sintering resistant material ( 22 ) is stable over the range of operating temperatures of the device ( 10 ), is not soluble with the underlying ceramic layer ( 16 ) and is applied by a process that is not an electron beam physical vapor deposition process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of U.S. Ser. No.09/245,262 filed on Feb. 5, 1999, now U.S. Pat. No. 6,203,927, and is acontinuation-in-part of U.S. Ser. No. 09/393,415, filed On Sep. 10,1999, now U.S. Pat. No. 6,296,945.

GOVERNMENT RIGHTS STATEMENT

This invention was conceived under United States Department of EnergyContract DE-AC05-950R22242. The United States Government has certainrights hereunder.

FIELD OF THE INVENTION

This invention relates generally to the field of thermal barriercoatings (TBC), and more particularly to a thermal barrier coating forvery high temperature applications, such as combustion turbine engines.In particular, this invention relates to the field of multi-layerceramic thermal barrier coatings resistant to sintering damage used forcoating superalloy components of a combustion turbine. These TBCs areapplied by inexpensive processes selected from the group consisting of:ceramic processing techniques, such as sol-gel techniques; vapordeposition techniques, such as chemical vapor deposition; and,preferably, thermal spraying techniques, such as air plasma spraying(APS), where induced vertical gaps in the TBC surface microstructure areprevented from sintering in service, to ensure strain tolerance duringuse.

BACKGROUND OF THE INVENTION

The demand for continued improvement in the efficiency of combustionturbine and combined cycle power plants has driven the designers ofthese systems to specify increasingly higher turbine inlet temperatures.Although nickel and cobalt based superalloy materials are now used forcomponents in the hot gas flow path, such as combustor transition piecesand turbine rotating and stationary blades, even these superalloymaterials are not capable of surviving long term operation attemperatures sometimes exceeding 1000° C.

It is known in the art to coat a superalloy metal component with aninsulating ceramic material to improve its ability to survive highoperating temperatures; see, for example, U.S. Pat. No. 4,321,310 (Ulionet al). It is also known in the art to coat the insulating ceramicmaterial with an erosion resistant material to reduce its susceptibilityto wear caused by the impact of the particles carried within the hot gasflow path; see, for example, U.S. Pat. No. 5,683,825 (Bruce et al.) andU.S. Pat No. 5,562,998 (Strangman). U.S. patent application Ser. No.09/393,417, filed on Sep. 10, 1999 (Docket No. T2-98-25,ESCM-283139-00223, Ramesh Subramanian), now U.S. Pat. No. 6,294,260,taught air plasma sprayed TBC coatings of 50 micrometer to 350micrometer thickness, applied to superalloy base substrates, for turbineapplication. There, the TBC coating had a planar grained microstructure,where an overlay was allowed to infiltrate the TBC bulk, completely orpartially fill microcrack volumes generally parallel to the superalloybase substrate, and finally react with the TBC material. This was toprovide a sintering inhibitor, as well as a coating with a low thermalconductivity, which is also erosion and corrosion resistant.

Much of the development in this field of technology has been driven bythe aircraft engine industry, where turbine engines are required tooperate at high temperatures and are subjected to frequent temperaturetransients as the power level of the engine is varied. A combustionturbine engine installed in a land-based power generating plant is alsosubjected to high operating temperatures and temperature transients, butit may also be required to operate at full power and at its highesttemperatures for very long periods of time, such as for days or evenweeks at a time. Prior art insulating systems are susceptible todegradation under such conditions at the elevated temperatures demandedin the most modern combustion turbine systems.

In particular, with regard to air plasma sprayed (APS) TBC's, due torepeated thermal cycling, these coatings have to readily accommodate thethermal expansion mismatch stresses and thermal strains to remainadherent to the superalloy substrate. Typical APS coatings achieve thisby porosity which is deliberately introduced during the depositionprocess, such as inter splat boundaries and micro-cracks within theceramic splats. With increasing demands for higher efficiency ofengines, the gas path temperatures are expected to rise and consequentlythe temperatures at the surface of the ceramic TBC. Higher temperatureswould then lead to accelerated sintering of cracks and pores in the APScoatings, especially at the surface. Sintering results in densificationof the coating and can lead to its early spallation, due to its reducedcapacity to accommodate thermal cycling. Stresses due to thermal cyclingcan be relieved by vertical cracks through the coating, which increasesthe thermal cyclic life of the coating.

These vertical cracks in APS coatings can result during the air plasmaspraying process, as described in the many articles published in thefield of thermal barrier coatings, for example, “Thermal Spray: Advancesin Coatings Technology— Experimental and Theoretical Aspects of ThickThermal Barrier Coatings for Turbine Applications,” G. J. Wilms et al.,Proceedings of the National Thermal Spray Conference, Sep. 14-17, 1987,Ed. D. L. Houck pp. 155-166. There, APS spraying at high substratetemperatures was described as inducing vertical segmentation crackswhich form while relieving shrinkage stresses within the deposited TBCupon cooling. Initiation of segmentation cracks during APS spraying athigh substrate temperatures of the TBC is shown in FIGS. 12 and 13 ofthe Wilms et al. article, where a brick-like microstructure is shown,and also in FIGS. 3 and 4 where a more monolithic structure is shown, asin FIG. 6. Preferred thick TBC's, over about 2 mm, are described asbeing dense, less than 15% porosity, but where individual planarplatelets are microwelded to each other and connected to their sublayerswith a fine network of vertical segmentation cracks, rather than beingporous, about 20% or greater porosity.

Coatings deposited by the APS process, with vertical cracks are calledsegmented TBCs. Formation of vertical cracks in APS coatings are alsodiscussed in U.S. Pat. Nos. 4,457,948; 5,073,433; 5,743,013 and5,839,586 (Ruckle et al., Taylor, Taylor et al. and Gray et al.,respectively), in European Patent 0 705 912 A2, and also in “CrystallineGrowth Within Alumina and Zirconia Coatings with Coating TemperatureControl During Spraying,” A. Haddadi et al., Thermal Spray: PracticalSolutions for Engineering Problems, C. C. Brendt (Ed.), ASMInternational, Materials Park Ohio, 1996, pp. 615-622; “Taguchi Analysisof Thick Thermal Barrier Coatings,” J. E. Nerz et al., Thermal SprayResearch and Applications, Proc. 3^(rd) National Thermal SprayConference, Long Beach Calif., 1990, pp. 669-673; and “EnhancedAtmospheric Plasma Spraying of Thick TBCs by Improved Process Controland Deposition Efficiency,” E. Lugscheider et al., Proc. 15^(th)International Thermal Spray Conference, 1998, pp. 1583-1588.

J. Wigren et al., in “A Combustor Can with 1.8 mm Thick Plasma SprayedThermal Barrier Coatings,” International Gas Turbine and AeroengineCongress and Exhibition Proceeding, American Society of MechanicalEngineers, 1998, pp. 1-10, taught a series of temperature cycles between330° C. and 340° C. over time to induce branched segmentation cracks,for thick protective TBC coatings on combustor walls. Such branchingswere also described by J. Wigren et al. in “Thermal BarrierCoatings—Why, How, Where and Where To,” Proceedings of the 15^(th)International Thermal Spray Conference, pp. 1531-1542, May 25-29, 1998,where it was pointed out that sophisticated TBC's have raised thetemperature capability of gas turbines by about 500° C. in the last 15years.

While these patents and articles discuss induced microcracks in ceramiccoatings, other articles discuss filling such microcracks, primarily toact as seals to corrosive agents, for example, “Effects of SealingTreatment and Microstructural Grading upon Corrosion Characteristics ofPlasma Sprayed Ceramic Coating,” Y. Kimura et al., Proc. 7^(th) NationalThermal Spray Conference 1994, pp. 527-536; “Sealing of Plasma SprayedCeramic Coatings by Sol-Gel Process,” K. Moriya et al., 7^(th) NationalThermal Spray Conference 1994, 549-553; and “Ceramic Impregnation ofPlasma Sprayed Thermal Barrier Coatings,” J. Karthikeyan et al., ThermalSpray: Practical Solutions for Engineering Problems, ASM International,1996, pp. 477-482.

The above-mentioned patents articles, however, do not address thepossibility of sintering the vertical cracks and the subsequent loss instrain compliance with increasing operating temperatures.

Accordingly, it is an object of this invention to make a device which iscapable of operating at temperatures in excess of 1200° C. for extendedperiods of time, with reduced component degradation. It is also anobject of this invention to provide a method of producing such a devicethat utilizes only commercially available material processing steps andinexpensive deposition techniques, such as APS, rather than electronbeam physical vapor deposition (“EB-PVD”). The APS process basicallyinvolves spraying TBC powders, such as stabilized zirconia, afterpassing them through a plasma gun.

SUMMARY

These and other objects of the invention are achieved by providing amethod for producing a device operable over a range of temperatureswhich comprises the steps: providing a substrate; optionally, coating abond coat layer on the substrate; coating a ceramic layer at least 50micrometers thick on the bond coat layer or the substrate by a processselected from the group consisting of ceramic processing techniques,vapor deposition techniques and thermal spray techniques, in a mannerthat provides said ceramic layer with a microstructure characterized bya plurality of vertical and horizontal gaps, where the vertical gapsprovide a columnar structure extending from the outer surface to atleast about ⅓ of the thickness toward the substrate; and depositing, atleast, within the vertical gaps a sintering inhibiting material, wherethe majority of vertical and horizontal gaps are not closed. If a bondcoat is not used, the ceramic layer can be applied directly to thesubstrate.

This invention has the potential to extend the operating temperaturecapabilities and durability of turbine engines beyond the current stateof the art, air plasma spray (APS) 8 wt. % yttrium stabilized zirconiaTBC. It involves the deposition of ceramic coatings with horizontaland-predominantly-vertical gaps and the infiltration of thesepredominantly vertical cracks with a sintering inhibitor. Upon operationat high temperatures, where sintering or closing up of the cracks couldoccur leading to a loss in strain tolerance, the sintering inhibitor isexpected to prevent closure of the vertical cracks. This will allow formaintenance of a strain tolerant TBC to higher surface temperaturesand/or extended periods of operation and consequently lead to improvedperformance. This invention provides a cost-effective alternative to theEB-PVD process.

The EB-PVD process is a very expensive technique compared to air plasmaspraying and this is primarily due to the requirement of a vacuumchamber to deposit the coatings and also the longer processing timerequired for the complete coverage of the turbine components. Acost-effective process is air plasma spraying and a microstructure withvertical cracks can be obtained by notifying the deposition parametersto yield segmented TBCs. Similar microstructures may also be processedby other coating techniques such as sol-gel and chemical vapordeposition “CVD” techniques. By introducing a sintering inhibitor, themultiphase coating system discussed in this disclosure becomes aneconomically very competitive thermal barrier coating system forapplication at high temperatures. Additionally, the selection processfor the composition of the base ceramic coating need not be constrainedby requirements specific to physical vapor deposition techniques, suchas minimum differences in vapor pressure between the constituents of theceramic composition. With the additional flexibility of utilizing plasmaspraying techniques, more complex parts can be handled when compared toEB-PVD coatings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a device, such as a turbine blade coatedwith a thick, air plasma sprayed ceramic thermal barrier layer;

FIG. 2 which best shows the invention, is a cross-sectional view of adevice having a thermal barrier coating in accordance with thisinvention, where a stable ceramic material is infiltrated onto thevertical and horizontal micro crack gaps resulting from air plasmaspraying; and

FIG. 3 is a greatly enlarged view of the surface of the thermal barriercoating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

When prior art thermal barrier coating systems are exposed to the hightemperature environment of the hot gas flow path of a land-basedcombustion turbine power plant, one of the reasons for failure of thethermal barrier coating is sintering of the ceramic TBC and consequentloss in strain tolerance. A current state-of-the-art thermal barriercoating is yttria stabilized zirconia (YSZ). The YSZ may be applied inthis invention by thermal spray processes such as new and improved airplasma spray APS, inductively coupled plasma processes, high power andhigh velocity plasma processes, or by vapor deposition processes such aschemical vapor deposition CVD, MOCVD, or by ceramic processingtechniques such as sol-gel, all now well known in the art. Thesetechniques can provide a predominantly vertical (in relation to thesubstrate) columnar microstructure at the outside surface of TBCs andalso create a series of submicron sized horizontal cracks within the YSZlayer intersecting the columnar microstructure. For the purposes of thisapplication, the terms “gap” is meant to include not only the gapsbetween adjacent columns in a columnar microstructure, but alsohorizontal cracks resulting from APS or similar processes. The amount ofvertical and horizontal gaps in the TBC can be accurately controlled bymodification of deposition parameters.

The gaps provide a mechanical flexibility to the ceramic TBC layer.During operation at high temperatures, it is known that these gaps havea tendency to close, and if the device is maintained at the elevatedtemperature for a sufficient length of time, the adjacent sides of thegaps will bond together by sintering. The bonding of the ceramicmaterial across the gaps reduces the strain compliance of the ceramiccoating, thereby contributing to failure of the coating duringsubsequent thermal transients.

Referring now to FIG. 1, one component device of a turbine is shown.Turbine blade 10 has a leading edge 13 and an airfoil section 17,against which hot combustion gases are directed during operation of theturbine, and which is subject to severe thermal stresses, oxidation andcorrosion. The root end 19 of the blade anchors the blade. Coolingpassages 21 may be present through the blade to allow cooling air totransfer heat from the blade. The blade itself 10 can be made from ahigh temperature resistant nickel or cobalt based superalloy 12, shownin FIG. 2, such as, a combination of Ni.Cr.Al.Co.Ta.Mo.W.

A bond coat 14 could cover the body of the turbine blade 12, which couldthen be covered by the thermal barrier coating 16, all shown in FIG. 2.The barrier layer of this invention, as well as the bond coat (or basecoat) and other protective coating can be used on a wide variety ofother components of turbines, such as, turbine vanes, turbinetransitions, or the like, which may be large and of complex geometry, orupon any substrate made of, for example metal or ceramic, where thermalprotection is required.

FIG. 2 illustrates a cross-sectional view of a portion of a devicehaving a thermal barrier coating, TBC 16, which is less susceptible to areduction of strain compliance due to sintering. Preferably the TBC 16will be at least 50 micrometers thick, to allow superior insulating andprotective properties for the underlying substrate. The device 10 has asubstrate 12 that may be made of a superalloy metal or other materialhaving the desired mechanical and chemical properties.

Disposed on the substrate 12 is an optional bond coat layer 14. In someapplications the bond coat layer 14 may be integral with the substrate12. In combustion turbine applications the bond coat layer 14 maytypically be an MCrAly layer deposited by an EB-PVD, sputtering or lowpressure plasma spray process. As is known in the art, the M in thisformulation may represent iron, nickel or cobalt, or a mixture thereof.Alternatively, the bond coat layer 14 may be platinum or platinumaluminide, or there may be no distinct bond coat layer. Disposed on thebond coat layer, or directly on the substrate 12 in the absence of abond coat layer 14, is a ceramic layer 16 which serves to thermallyinsulate the substrate 12 form the hostile environment in which itoperates. The ceramic layer 16 is preferably formed of a YSZ material,for example 8 weight % yttria stabilized zirconia as is known in theart, or other TBC material, deposited by a new and improved APS process,to form a columnar microstructure characterized by a plurality of gaps18 between adjacent columns 20 of YSZ or other material. An oxide scale15 is also shown, being formed from the bond layer 14, and which furtherprotects the substrate from oxidative attack. As shown, the columns 20provide a columnar structure extending from the outer surface 23distance 25 which is at least about ⅓ of the thickness toward thesubstrate 12.

As shown in FIG. 3, the TBC layer of the device also includes asintering inhibiting material coating 22 disposed within thepredominantly vertical gaps 18, but not generally bridging across thegaps from one column to the adjacent column. This sintering inhibitingmaterial 22 will also coat the generally horizontal gaps 30. Bysintering resistant material in this application it is meant anymaterial which is more.resistive to sintering than the TBC material 12.The sintering inhibiting material 22 may be a ceramic material that isstable over the range of temperature in which the device 10 is operated,for example ambient air temperature to over 1200° C., and as high as1500° C. By stable in this application it is meant that the materialdoes not undergo a crystallographic phase transformation when exposed tothe full range of its design operating temperatures.

U.S. Pat. NO. 5,562,998 (Strangman) discussed previously teaches theapplication of a bond inhibitor coating over a ceramic thermal barriercoating. The bond inhibitor described in that patent is an unstabilizedmaterial, such as unstabilized zirconia or unstabilized hafnia. Thesematerials will sinter or bond together during high temperatureoperation, but upon cooling to lower or ambient temperatures, thesematerials will cycle through a disruptive tetragonal monoclinic phasetransformation. This transformation tends to break the bonds betweenadjacent columns. While such materials may be effective for aircraftengines that have short thermal cycles, they may be unsuitable for landbased power generating engines which have longer operating cycles.During long term exposure to high temperatures, unstabilized zirconiaand hafnia will dissolve into the underlying YSZ material.

Once dissolved into the ceramic insulating material, the bond inhibitormaterial of the U.S. Pat No. 5,562,998 is no longer available to undergoa crystallographic transformation within the gaps upon cooling. Thus,after extended periods of high temperature operation, the sintered bondsare not broken, consequently reducing the strain compliance of theceramic insulating material and leading to premature failure of thecomponent.

Furthermore, prior art U.S. Pat. No. 5,683,825 (Bruce et al.), discussedabove, discloses an erosion resistant thermal barrier coating. In thatpatent, an erosion resistant composition such as alumina or siliconcarbide is disposed on top of a ceramic insulating layer. That patentdescribes a relatively thick coating of erosion resistant material thatdoes not penetrate between the columns of the underlying ceramicinsulating material, and therefore does not act to prevent sinteringbetween the columns.

The sintering inhibiting material 22 of the present invention overcomesthese deficiencies in the prior art. By infiltrating a sinteringinhibiting material 22 into the gaps 18 and 30 and preventing thebonding of adjacent columns 20, there is no need to rely upon acrystallographic transformation to break the bonds as in the prior art.Sintering inhibiting material 22 is preferably an oxide compound whichis insoluble with the underlying ceramic layer 16, and which is stableover the range of temperatures of operation of device 10. One suchsintering inhibiting material 22 for use with a ceramic layer 16 of YSZis aluminum oxide (alumina) Al₂O₃. An alternative embodiment for thesintering inhibiting material 22 is yttrium aluminum oxide.

The sintering inhibiting material 22 may be infiltrated into the gaps 18via a metal organic chemical vapor deposition (CVD) process. The CVDprocess is used to deposit the sintering resistant material 22 to athickness on the top surface 23 of the columns 20 of ceramic layer 16 ofYSZ is aluminum oxide (alumina) Al₂O₃. The sintering inhibiting material22 may be infiltrated into the gaps 18 via a metal organic chemicalvapor deposition (CVD) process. The CVD process is used to deposit thesintering resistant material 22 to a thickness on the top surface of thecolumns 20 of ceramic layer 16 ranging from no more than a few angstromsto several micrometers. In one embodiment an alumina layer having athickness of approximately 5 micrometers on the top surface of thecolumns 20 of the ceramic layer 16 may be used. Alternative embodimentsmay have a thickness of sintering resistant material on the top surfaceof the columns 20 of ceramic layer 16 of no more than 0.1 micrometer, oralternatively no more than one micrometer, or alternatively no more than10 micrometers. The thickness of the coating of sintering resistantmaterial 22 within the gaps 18 will be less than but generallyproportional to the thickness on the surface of the ceramic layer 16.The thickness should be controlled to prevent the sintering resistantmaterial 22 from bridging across the gaps 18, such as shown at points 34thereby degrading the performance of the coating. Because the selectedsintering inhibiting material 22 does not readily sinter, the columns 20of device 10 will not bond at high temperatures. And because thesintering inhibiting material 22 is not soluble with the underlyingmaterial of ceramic layer 16, it is maintained at the surface of thecolumns 20 throughout the life of the device 10, thus maintaining itsresistance to sintering.

The sintering inhibiting material 22 may be applied to the insulatingceramic layer 16 as an intermediate amorphous or unstable phase. In oneembodiment of the invention, amorphous alumina is deposited within thegaps 18 by a metal organic CVD process. Upon heating, either during themanufacturing process or during the initial operation of the device 10,the amorphous coating undergoes a transformation to acrystallographically stable phase, such as alpha Al₂O₃. It is alphaphase that is stable at high temperatures and that performs the functionof a sintering inhibitor.

The method for producing a device according to this invention utilizesprocesses that are commercially available. To produce such a device, asubstrate 12 may, optionally, first be coated with a bond coat 14, ordirectly onto the substrate if no bond coat is used, by a known processsuch as a low pressure plasma spray, high velocity oxygen fuel, shroudedplasma spray or air plasma spray process. The ceramic TBC layer 16 isthen disposed on the bond coat 14 by known improved APS processes whichsimultaneously utilizes a plasma to melt the ceramic particles of acarrier gas and to deposit the particles onto the substrate. Severalmodifications to the spray parameters—such as voltage, current, particlevelocity and substrate temperature—can control the function ofhorizontal and vertical cracks.

This improved APS process provides a ceramic TBC layer 16 having aplurality of gaps 18 and 30 therewithin. The sintering inhibitingmaterial 22 is then applied to the surface of the columns 20 by a vapordeposition technique such as chemical vapor deposition or metal organicCVD, or by one of a number of known infiltration techniques such assol-gel infiltration.

Preferably, the sintering inhibiting material 22 may be applied as acontinuous coating within the gaps 18, either as an amorphous or astable phase. FIG. 2 illustrates an alternative embodiment of a devicein accordance with this invention. Like structures are numberedconsistently between the two Figures. As seen in FIG. 2, a substrate 12having an optional bond coat 14 disposed thereon is coated with aceramic layer 16.

While not shown in the drawings, the inhibiting material can also bedisposed within the gaps 18 as a plurality of nodules which maydemonstrate a reduced tendency to form bridges between column 20 due toa lesser contact area between nodules on adjacent columns when comparedto a continuous coating of sintering inhibiting material. However, anyformation of intermittent bridges between columns 18 can break easilyupon regular thermal cycling of device 10. The nodular morphology isachieved by controlling the thickness of the applied coating of materialand the subsequent heat treatment. For example, a relatively thincoating of approximately 0.1 micrometer of alumina at the top surface 23of the ceramic layer 16 will result in a relatively thin continuouslayer in the gaps 18.

During the subsequent heat treatment, as the alumina converts to thestable alpha phase it undergoes a volume reduction which tends to createnodules of sintering resistant material within the gaps. A thickercoating of approximately 1 micrometer of alumina at the surface willprovide a thick enough coating within the gaps 18 that even after heattreatment the sintering resistant material 22 to remain as a continuouscoating. An alternative method of achieving a continuous coating withinthe gaps 18 is to apply multiple thin layers of the sintering resistantmaterial so that any space is essentially filled with to create acontinuous coating 22.

In the embodiment of FIG. 3, the sintering inhibiting material isdisposed within only a top portion of gaps 18 and not a bottom portionof gaps 18. The geometry of the gaps 18 and the process for depositingthe coating will control this variable. Preferably in this process theimproved APS process will cause the sintering inhibiting material tocoat the interior gaps 18 and 30 to a substantial extent, at least{fraction (1/10)} the thickness of the thermal barrier layer 16.

Other aspects, objects and advantages of this invention may be obtainedby studying the Figures, the disclosure, and the appended claims.

What is claimed is:
 1. A method for producing a device operable over arange of temperatures, the method comprising the steps of: providing asubstrate; coating a ceramic layer over the substrate in a manner thatprovides said ceramic layer with a microstructure characterized by aplurality of vertical and horizontal gaps and depositing within only atop portion of said vertical gaps a sintering inhibiting material. 2.The method of claim 1, wherein the step of depositing a sinteringinhibiting material flirter comprises depositing a sintering inhibitingmaterial that is stable over said range of temperatures, and wherein abond coat layer is applied to the substrate.
 3. The method of claim 1,wherein the step of depositing a sintering inhibiting material furthercomprises the step of depositing a sintering inhibiting material that isinsoluble with said ceramic layer.
 4. The method of claim 1, wherein thestep of depositing a sintering inhibiting material further comprisesdepositing said sintering inhibiting material as a continuous coatingwithin said gaps.
 5. The method of claim 1, wherein the step ofdepositing a sintering inhibiting material further comprises depositingaluminum oxide.
 6. The method of claim 1, wherein the step of depositinga sintering inhibiting material further comprises depositing yttriumaluminum oxide.
 7. The method of claim 1, wherein said ceramic layercomprises a segmented microstructre, and wherein the step of depositinga sintering inhibiting material further comprises depositing saidsintering inhibiting material on a surface of columns of said ceramiclayer to prevent the sintering of gaps during the operation of saiddevice.
 8. The method of claim 1, wherein the step of depositing asintering inhibiting material further comprises the steps of: depositinga sintering inhibiting material in an unstable phase; and heat treatingsaid sintering inhibiting material to obtain a sintering inhibitingmaterial which is stable over said temperature range.
 9. The method ofclaim 1, wherein the step of coating the ceramic layer is performed by aprocess selected firm the group consisting of air plasma spraying,chemical vapor deposition and sol-gel techniques.
 10. The method ofclaim 8, wherein the step of heat treating is performed during theoperation of said device.
 11. The method of claim 9, wherein the step ofcoating the ceramic layer is by air plasma spraying.
 12. A method ofproducing a device operable over a range of temperatures, the methodcomprising: providing a substrate; coating a ceramic layer over thesubstrate in a manner that provides the ceramic layer with amicrostructure characterized by a plurality of vertical and horizontalgaps; and depositing within only a top portion of at least some of thevertical gaps a sintering inhibiting material configured as a pluralityof nodules that form a discontinuous coating on the ceramic layer. 13.The method of claim 12, wherein the nodule morphology is formed bycontrolling the coating thickness of the sintering inhibiting materialand the subsequent heat treatment of the sintering inhibiting material.14. The method of claim 13, wherein the nodule morphology is controlledby depositing about 0.1 micrometer of the sintering inhibiting materialat a top surface of the ceramic layer to form a relatively thincontinuous layer of the sintering inhibiting material in the gaps andthen allowing the sintering inhibiting material to convert to a sablealpha phase during the subsequent heat treatment, such that thesintering inhibiting material undergoes a volume reduction which createsnodules of the sintering resistant material within the gaps.
 15. Themethod of claim 12, wherein the step of coating the ceramic layer isperformed by a thermal spray technique.
 16. The method of claim 12,wherein the step of coating the ceramic layer is performed by a vapordeposition technique.
 17. The method of claim 12, wherein the sinteringinhibitor material comprises aluminum oxide.
 18. The method of claim 12,wherein the sintering inhibitor material comprises yttrium aluminumoxide.